Photographic bleach-out layer



Patented Apr. 4, 1944 UNITED STATES PATENT OFFICE I PHOTOGBAPHIC BLEACH-OUT LAYER Henry 0. Staehle, Rochester, N. E, minor to Eastman Kodak Company,

corporation of New Jersey Claims.

My invention relates to light-sensitive layers for photography, and more particularly to lightsensitive layers for the so-called bleaching out" process of photography.

As is well known, the bleaching-out. process of photography primarily consists of exposing to light a layer containing a. dye capable of being decolorized under influence of light. Various substances have been used in this process for the purpose of speeding up the printing of the photographic layer and the bleaching of the dye therefrom. For instance, hydrogen peroxide has been used to accelerate the bleaching, but due to the fact that it rapidly decomposes into oxygen and water, it is of little or no use. Similarly, metal peroxides such as barium peroxide have been tested'as bleaching accelerators, but have been found to beof little or no use.

In a bleaching-out process in. which the accelerator is incorporated in the photographic layer along with the dye, the special characteristics which the bleaching accelerator must have are thatit will keep indefinitely in intimate contact with the dye without adverse eiiects upon the dye, and yet is or may be caused to be available when required for bleaching. To meet these requirements, the accelerator should be relatively stable and non-volatile. Moreover, after the accelerator hasserved its purpose, it should be readily removable from the layer to prevent further bleaching of the dye in the unexposed area of the layer. It is now apparent why a relatively unstable peroxide such as hydrogen peroxide is unsuitable for the purpose.

Peroxide compounds relatively more stable than hydrogen peroxide, such as solid peroxides, would be suitable for use in the process since they have relatively low vapor pressures and are, therefore. substantially non-volatile under ordinary conditions.

One object of the present invention is to provide a photographic material for use in the bleaching-out process of photography.

Another object is to provide bleaching accelerator compounds of particular use in bleachins-out layers.

I have discovered a class otperoxide compounds, namely, solid organic peroxides which are eminently suitable for use in the bleaching- I out process and especially suitable for incorporation into bleaching-out layers. Typical solid organic peroxides which are found to besuitable for use in my invention are, ior example, benzoyl acetyl peroxide, and tetralin peroxideI-Ielv. Chim. Acta 15, 1390 (1932), and others.

These peroxides, especially benzoyl peroxide, have the property of being relatively stable in the dry state; however, upon treatment with moisture they gradually'decompose into ouanic acid and hydrogen peroxide. This property is especially useful in my process as will be apparent from the following description.

In the manner of my invention the peroxide compound is incorporated into the photographic layer along with the dye and the layer kept in the dry state until it is desired to make an exposure, then the layer is first moistened, then exposed, and finally treated with further moisture in the absence .of strong light to decompose the residual peroxide compound.

The photographic layer may contain as the hindingagent a high molecular weight colloidal material such as natural or synthetic resins, cellulose esters and the like. For example, cellulose nitrate or acetate, cellulose mixed esters, such as cellulose acetate propionate, resins such as polyvinyl acetate, cellulose others, etc. are

suitable.

The following examples illustrate my invention.

Example 1 ii baryta paper is coated with a solution oi the following composition:

After curing the paper it is stored in a dry place until required for use. The cellulose nitrate used in the above formula is a low viscosity highly alcohol soluble nitrate of nitrogen content of about 11 per cent. Before exposure the paper is moistened by exposure to humid air and following this exposed to strong light under asuitable pattern and finally exposed further to moist air to decompose the peroxide compound remaining in the layer. The paper is then dried. Where the colored layer has been exposed to light, the dye will be markedly destroyed. The

unexposed portions will be relatively unaffected.

The principal function of the peroxide is to inperoxlde, acetyl benzoyl peroxide, ascaridol, crease the rate of bleaching, that is. y having the peroxide present, the dye is bleached in a fraction oi the time required when no peroxide is used.

' Example 2 Grams Polyvinyl acet Methyl alonhnl Methylene Blue Benzoyl pernxifln If desired, the paper may first be coated with the composition of Example 1, minus either the dye or peroxide compound, followed by a coating from the solution of Example 2 containing either dye or peroxide compound depending upon which was used in the undercoat. After curing, the paper is stored in a dry place. The bleaching-out paper thus prepared may be processed as described in Example 1.

Example "3 A baryta paper is coated with a subbing layer from a composition such as shown in Example 1, preferably containing no dye or peroxide compound. This subbing layer is then overcoated with a bleaching-out'layer containing cellulose acetate 38 per cent acetyl, as the binding agent, from the following solution.

Grams In theproduction of other bleaching-out papers prepared in a manner similar to that shown in the preceding examples, other organic peroxide compounds may be used in place of benzoyl peroxide, and similarly, other dyes maybe substituted for the particular dye of the examples. In addition, it it is so desired, instead of coating a baryta paper one may use "for the supp rt a cellulose ester as, tor example, cellulose nitrate and coat this support with a' solution or dye, organic peroxide compound and cellul'osic or resin binder from a solvent combination such as shown in Example 1. It is not necessary that the coating composition be entirely free from water since peroxides are slowly decomposed in water. A-

cordingly, other binding agents which can be coated from aqueous organic solvent solution are suitable for use in the layers of my invention.

Other dyes suitable for use in the bleaching-out layers or my invention may for example be Rhodamine, Curcumin, Brilliant Green, Pyronine G, Rosinduline, etc.

Obviously, my invention is not limited to the foregoing examples or the described methods given therein, and Kris tobe understood that the agent, a bleaching-out dye, and a solid organic peroxide compound as an accelerator for bleaching said dye, and coating a layer from the composition.

2. The method of forming a photographic layer for the bleaching-out process which comprises dissolving in organic solvent medium substantially free of water, a binding agent, a bleachingout dye, and a solid organic peroxide compound as an accelerator for bleaching said dye, and coating a layer from the composition.

3. The method of forming a photographic layer for the bleaching-out process'which comprises dissolving in organic solvent medium a binding agent, a bleaching-out dye, and benzoyl peroxide as an accelerator for bleaching said dye, and coating a layer from the composition.

4. The method of forming pictures in the bleaching-out process of photography which comprises moistening a photographic layer having a binding agentand uniformly dispersed therein a bleaching-out dye and a solid organic peroxide as an accelerator tor bleaching said dye, exposing said layer througha pattern, and treating.

.layer through a pattern, and treating said layer with additional moisture to decompose any undecomposed peroxide in the layer.

HENRY c. srAnr-nn. 

